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Light colored scalars from grand unification and the forward- backward asymmetry in t t-bar production

The experimental results on the $t \bar t$ production cross section at the Tevatron are well described by the QCD contributions within the standard model, while the recently measured forward- backward asymmetry is larger than predicted within this framework. We consider light colored scalars appearing in a particular SU(5) grand unified theory model within the 45- dimensional Higgs representation. A virtue of the model is that it connects the presence of a light colored SU(2) singlet ($\Delta_6$) and a color octet weak doublet ($\Delta_1$) with bounds on the proton lifetime, which constrain the parameter space of both scalars. We find that both the total $t \bar t$ production cross section and the forward-backward asymmetry can be accommodated simultaneously within this model. The experimental results prefer a region for the mass of $\Delta_6$ around 400 GeV, while $\Delta_1$ is then constrained to have a mass around the TeV scale as well. We analyze possible experimental signatures and find that $\Delta_6$ associated top production could be probed in the $t \bar t$ + jets final states at Tevatron and the LHC.

12.10.Dm; 13.85.Ni; 14.65.Ha

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